The present invention relates in general to the field of coal-fired power stations having a dry firing, and in particular to an arrangement for separating coarse ash out of a flue gas stream, a separator sieve being disposed in a flue gas channel that leads to a catalytic converter for reducing the NOx level and/or a heat exchanger for pre-heating combustion air.
During dry firings in a coal-fired power plant, ash is produced as dry dust that is partially carried along by the flue gas stream. As a function of the type of coal and the temperature distribution within a combustion chamber, an exceeding of the ash-softening point can occur locally. As a result, the originally dry and pulverous ash particles stick together or even sinter together. The resulting coarse ash particles (popcorn ash) can, as is known, clog the channel walls of catalytic converters, provided for reducing the NOx level, of flue gas cleaning devices, and/or can lead to significant pressure drops in the catalytic converter, in the following air pre-heater and/or in the electrostatic filter.
Commonly owned U.S. Pat. No. 6,994,036 discloses separating coarse ash out of the flue gas stream, before it reaches the catalytic converter, with the aid of a sieve arrangement that can be pivoted out of a rest position against the effect of a return force. The flue gas stream is subjected to constant, slight vibrations that suffice to cause movements or vibrations at the sieve arrangement. This causes the coarse ash particles that have been separated off on the sieve and adhere to the sieve surface to be shaken off.
With this known arrangement, the separator sieve is disposed approximately vertically at the inlet of a flue gas channel. The coarse ash particles are shaken off into an ash hopper that precedes the sieve.
At high flue gas flow velocities, the metallic meshes of the known separator sieve are subjected to considerable abrasion effects from ash particles that strike the sieve and pass through the sieve. Due to this abrasion effect, sieve openings result through which the coarse ash can pass, thereby partially reducing the separation function of the sieve arrangement. For this reason, in order to maintain their separation function, such separator arrangements must be checked, serviced and possibly replaced, whereby the power plant must sooner or later be briefly shut down.
By using separator modules that at the in-flow side are made of a material having a high mechanical wear resistance, such as a ceramic or sintered material, the durability of the sieve arrangement in flue gas channels can be considerably improved at high flue gas flow velocities. Due to the large dimensions of the sieve cross-sections in the flue gas channel, such sieve arrangements of wear-resistant materials entail considerable manufacturing costs.
It is therefore an object of the present invention to provide a separator arrangement that is economical to produce, and that even at high flue gas flow velocities in the flue gas channel enable an excellent separation function and operation that is favorable with respect to maintenance.